1.They said when it is put on top of something, two things happen.
on top of在…上边;在…上方
There was an unappealing film of slime on top of the pond.
池塘表面有一层黏腻腻的污泥 。
2.Just 10 to 20 square meters of this material on the rooftop could nicely cool down a…house in summer.
cool down(使)变凉;冷静下来
Cool down very gradually after working up a sweat.
大量出汗后要慢慢降温 。